My question is that since its the same celestial I summon each time I use find steed must I choose the same type of mount, or could the first summoning be a warhorse and the next time a camel?
You always summon the same steed.
When the steed drops to 0 hit points, it disappears, leaving behind no physical form. You can also dismiss your steed at any time as an action, causing it to disappear. In either case, casting this spell again summons the same steed, restored to its hit point maximum.
You have the option to release it completely from its bond, at which point you can cast the spell again to summon a new steed of a new form.
You can't have more than one steed bonded by this spell at a time. As an action, you can release the steed from its bond at any time, causing it to disappear.